Automatic Charging relay

J

Jamie 10017

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Joined
Nov 13, 2011
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32751
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I need some advice on a Automatic Charging Relay I don't need anything fancy. I have Twin Engines and 105 amp alternators. I was thinking 3 batteries 1 start and 2 house batteries but I'm open to ideas, suggestions, advice. Does anyone use them ? Pros Cons I haven't bought anything and I'm looking for ideas to plan this out . I don't know much about them and I know there are some really good people on here that will be straight up with me about them.. Thanks Jamie
 
In very general terms, a good "generic" plan is as follows: One start battery for each engine, and one house bank. Note that the house bank may be comprised of multiple parallel wired batteries.

An ACR operates as follows:

When the first battery n he charging train is not fully charged ( ie: voltage below a certain threshold ) the relay connecting he next step in the train is open ( ie: not connected ). Once the first battery regains a full charge ( as represented by a high enough voltage ), the relay will engage and make the connection to the next ( and one presumes, not yet fully charged ) battery in the train. This allows the second battery to be charged.

Which brings us to the choice of "which battery is the primary ( first charged ) and which is secondary. Many would say the the relatively small start battery should be charged first, then letting the "overflow" charge the house. I actually prefer the reverse order. Charge the large house first, then charge the start battery. Reason: Connecting the charger AND the fully charged primary to the secondary will cause the current to flow from the primary battery along with the charger current to the secondary. By placing the larger bank as primary, the percentage of stored charge sent to charge the less charged secondary is lower. ( Note: per cent. )

I have used ACRs as well as isolators and prefer the ACR. In theory, an isolator is much more elegant, and does exactly what you want; in practice, the ACR performs better.

There are situations where things can get complex. If you have twin engines ( two charge sources ), with a start battery each, and a single large house battery bank, things are not so simple. ( Isolators work best in this configuration, but the right isolator for the task is difficult to find and pricey ).

I hope others will add their thoughts on this as well. Mine comments relate to my knowledge and experience, but are far from the last word on the topic.

--

Note: you must use the same chemistry/type" throughout. That is, all must be flooded lead acid, or all must be AGM lead acid and so forth. Do not, for example, mix one AGM with one flooded.
 
Isolating starting from house loads is something I would do on just about any vessel I needed to start at.will. The place to start such a project though is to begin with your planned loads and plan for charging. That will tell you the size of your batteries and charging capacity. That in turn will tell you your needed battery size and types. That finally will strongly suggest your isolating components.

An acr is a god device as it eliminates the voltage drop associate with diode based isolators. But, there are dc to dc chargers that will intelligently charge a different battery type if needed. Check out balmar for example. Many/most systems will not need such a system, but they do exist. Often, You end up using these components if you have to achieve a more significant capability without increasing alternator sizes, etc. To say it another way, if you don't do your fundamental planning up front and size your overall system to achieve your goals with simplicity, you may find yourself with a more complicated system later trying to make up for it.
 
Isolating starting from house loads is something I would do on just about any vessel I needed to start at.will. The place to start such a project though is to begin with your planned loads and plan for charging. That will tell you the size of your batteries and charging capacity. That in turn will tell you your needed battery size and types. That finally will strongly suggest your isolating components.

An acr is a god device as it eliminates the voltage drop associate with diode based isolators. But, there are dc to dc chargers that will intelligently charge a different battery type if needed. Check out balmar for example. Many/most systems will not need such a system, but they do exist. Often, You end up using these components if you have to achieve a more significant capability without increasing alternator sizes, etc. To say it another way, if you don't do your fundamental planning up front and size your overall system to achieve your goals with simplicity, you may find yourself with a more complicated system later trying to make up for it.
 
Playing off what has already been asked and what radioactive said he prefers by making the start bank the second bank, it is my understanding that in normal situations when leaving the dock after the banks are all 100% charged from the 120V charger, that bank #2 can draw off number one until it's voltage gets too low. This effectively means that your new starting banks are effectively 4 batteries (assuming the house bank is fully charged), which puts even less strain on the batteries, maintaining higher voltages (less voltage drop) to the starter. Am I correct in this reasoning? I've been considering doing this same thing on my boat, knowing how the ACR works, but looking at it from what I believe is what radioactive is saying, I'm leaning towards his method.

2nd question related but not identical: is it possible to wire two ACR's together, such that alternator supplies ACR #1, which charges a starting bank and then the second output of ACR #1 feeds input on ACR #2, which can then charge a house bank and a separate inverter bank? Thinking about future plans of installing an inverter, but will want to keep my starting banks, house 12V, and inverter bank separate.
 
Why the house and inverter bank separate?

Another question, maybe I missed it, but why the relay when you have twin engines and twin alternators? I could see if you are using one alternator to charge a separate starting battery for each motor. But that does not sound like what you want to do.

I have two alternators and two 8D batteries. One for each motor tied to its own alternator. One is also the house bank. Both can be tied together for the house via one combining switch or for the motors via another combining switch in the engine room or a switch on the dash. Is that what you have now?
 
The desired charge path is as follows:

Alternator #x --> Selected primary bank --> ACR --> Selected Secondary bank ( --> ACR --> repeat if needed. Really! )

As for making the decision of which bank is primary, you are correct that, when beginning at the dock ( and shore power charger ) you should have all banks fully charged. In my case, I overnight, without any other power source, so when it is time to pull the hook and go home, the starter bank should be full or very nearly so, but the house bank may be assumed to be moderately to heavily discharged. In this case, it makes sense to charge the most discharged, percentage wise, bank (house) first, then "top off" the secondary (start). YMMV. Each vessel has it's own particular needs.

The only time ( that I am aware of! ) that things get weird, electronically, is when you have two ( or more ) alternators that both end up charging ( for instance ) a single house bank. At that point, you have two independent charge sources attempting to adjust their charge rate based on the target voltage. It is very unlikely that the two alternators will have identical charge profiles. I have NO evidence, but I suspect that the result is that one alternator will provide full output and one will idle. I am not sure, and do not care to test... But is should be considered by someone with a greater knowledge on the topic than I have. My personal solution was to not allow this to occur.

--edit--
"Why the house and inverter bank separate? "

Likely because the inverter bank has large and intermittent ( perhaps ) voltage fluctuations as well as large current requirements. The "house" would generally have low/moderate current needs and would have a smooth voltage level.

Another is the way some users use the inverter bank; that is use to depletion. With separate banks, you would lose whatever is on the inverter, but the cabin lights and nav instruments remain functional.

I am sure that are other reasons as well.
 
There is a wise saying, you can never have too much battery AH's when it comes to a house bank. I use the same bank for my house and the inverter system. My inverter will also recharge the house bank with up to 130 amps of DC when in bulk mode. I almost never use my inverter as an inverter its primary use is the house bank's genset or AC dockside charger.
I use and and like BlueSea ACR's. The proper ACR with a control switch will allow parallel starting when needed. Most of the time when cruising I leave the ACR in the automatic mode. The BlueSea unit allows you to choose which battery bank is the primary bank by simply changing the sense wire's position.
Bill
 
I am one of the many that charges the cranking battery first. With a cranking battery that just needs topping off an ACR will close quickly and start on the house charging. If the ACR cycles a few times when the depleted house bank sucks the system voltage down fine. I know my cranking side is maintained at good voltage.

I know with Yandina's combiners you can certainly charge wet battery banks and AGM banks from the same source. I would think with other setups as well.
 
"you can certainly charge wet battery banks and AGM banks from the same source." -- KinCal

Yes. You can.

It is better if you do not. AGMs offer better performance in several areas, but but grouping them with flooded you negate some of those desirable characteristics.
 
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